1. Field of the Invention
The present invention relates to a thin film magnetic head, a thin film magnetic head assembly, a storage device, and a method of manufacturing a thin film magnetic head.
2. Related Background Art
With increase in density of magnetic recording media such as hard disk drive and the like, there are increasing demands for improvement in the performance of the thin film magnetic heads. The thin film magnetic heads include reproducing heads having a magnetoresistive element (hereinafter referred to as an MR (Magneto Resistive) element) for readout. The reproducing heads are required to have the property of low Barkhausen noise. In order to decrease the Barkhausen noise, there is a known technique of placing hard magnetic layers on the both sides of the MR element and applying a bias magnetic field to the MR element to bring a free layer in the MR element into the single domain structure.
Incidentally, when the hard magnetic layers are placed so as to sandwich the MR element (the free layer) between them, there appear regions where directions of magnetization are fixed by magnetic fields from the hard magnetic layers to disable detection of magnetic fields of signals (hereinafter referred to as dead zones), in the vicinity of end regions adjacent to the hard magnetic layers, in the MR element. For this reason, in the case where a pair of electrode layers for supplying an electric current (sense current) to the MR element are placed so as not to overlap with the MR element, the supplied current passes the dead zones, posing the problem of decrease in output from the reproducing head. In order to solve this problem, there is a known technique of placing the electrode layers so as to overlap in part with the MR element (e.g., reference is made to Japanese Patent Applications Laid-Open No. 08-45037, No. 09-282618, No. 11-31313, No. 2000-76629, and so on).
When the electrode layers are placed so as to overlap with the MR element, the current becomes reluctant to flow through the dead zones in the MR element and thus those zones do not contribute directly to the output of the reproducing head. However, since the regions of the MR element overlapping with the electrode layers absorb the magnetic field leaking from the magnetic recording medium, the absorbed magnetic field is transmitted up to the highly sensitive region in the central part of the track, thereby posing the problem of read blur to expand the effective track width. As a solution to this problem, Japanese Patent Application Laid-Open No. 2001-176032 discloses a technique of providing a portion of a magnetosensitive layer (free layer) antiferromagnetically exchange-coupled with a ferromagnetic metal layer through a metal layer to decrease the reproduction sensitivity of that portion.